Vehicle fuel systems include evaporative emission control systems designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel.
In hybrid-electric vehicles, the fuel tank is typically sealed with a fuel tank isolation valve (FTIV). Prior to refueling, fuel vapors in the tank may be vented to the fuel vapor canister by opening the FTIV. During the refueling event, the FTIV is maintained open, so that fuel vapor generated during refueling can be shunted to the canister. Air stripped of fuel vapor is directed to atmosphere via a canister vent line.
However, the canister vent line is prone to becoming restricted due to sand, salt, spiders, etc. entering the conduit. A blocked or restricted vent line may limit the flow of stripped air out of the canister, leading to a fuel tank back pressure. In turn, the fuel tank back pressure may result in a pre-mature shutoff (PSO) of the fuel dispenser. Restrictions at other points in the vent pathway, and other conditions where the rate of refueling vapor generation is greater than the rate of air flow out of the canister vent line can also cause PSOs. Refueling operators made become agitated as the fuel dispenser continually shuts-off before the fuel tank is filled.
The inventors herein have recognized the above issues and have developed systems and methods to at least partially address them. In one example, a method for a fuel system, comprising: during a first condition, directing gasses stripped of fuel vapor from a fuel vapor canister to an engine intake while maintaining a fuel tank isolation valve open. By directing the gasses stripped of fuel vapor the engine intake, a restricted vent line may be bypassed during a refueling event. In this way, premature shutoff events may be mitigated, allowing for a continuous refueling event.
In another example, a method for refueling a vehicle, comprising: depressurizing a fuel tank; removing an access restriction to a fuel filler neck; and responsive to a fuel tank pressure increasing above a first threshold, opening a canister purge valve. In PHEVs, the PCM must stay active during a refueling event in order to depressurize the fuel tank and remove access restrictions to the fuel filler neck, and thus may perform additional mitigating action during the refueling event. In this way, by opening the canister purge valve prior to the fuel tank pressure increasing above a first threshold, gasses stripped of refueling vapors may continue to exit the fuel vapor canister, preventing an increase in back pressure that may otherwise trigger a premature shutoff event.
In yet another example, a fuel system for a vehicle, comprising: a fuel tank comprising a fuel filler neck, a fuel vapor canister coupled to the fuel tank via a fuel tank isolation valve; a canister purge valve coupled between the fuel vapor canister and an engine intake; a canister vent line coupled between the fuel vapor canister and atmosphere; and a controller configured with instructions stored in non-transitory memory, that when executed, cause the controller to: during a first condition comprising a refueling nozzle engaged with the fuel filler neck and dispensing fuel into the fuel tank, opening the fuel tank isolation valve; and responsive to a fuel tank pressure increasing above a first threshold, opening the canister purge valve. By opening the canister purge valve when a fuel tank pressure increases above a first threshold, the fuel system can manage refueling vapors even when the rate of fuel vapor generation exceeds the rate of gas flow out of the canister vent line. In this way, the fuel system may be refueled by dispensers with high rates of fuel dispensation without the fuel dispenser shutting off prematurely.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.